1. Technical Field
The present invention relates to a method to assign an upstream timeslot to a network terminal, an arrangement adapted to perform this method, and a communication system wherein the method is used.
2. Discussion of Related Art
Such a method and related arrangement are already known in the art, e.g. from the U.S. Pat. No. 5,539,743, entitled `Multiple Access System for Communication Network`. Therein, a communications system is disclosed wherein a plurality of network terminals, named substations, are coupled to a main station via a network with multipoint-to-point architecture. A substation upon request is assigned an upstream timeslot that is used for transmission of an upstream data burst towards the main station. This is done by the main station which downstream broadcasts so called data transmission enable signals (TENO) or grant messages that define for each upstream timeslot to which substation it is assigned. The main station keeps track of a time table or grant table wherein the different substations occupy entries based on their requests for upstream bandwidth. This table is scanned at regular time intervals and the substation whose identifier is stored in the scanned entry is assigned a timeslot via a grant message. As indicated in column 11, lines 30-37, of the cited United States Patent, the main station gives authority to an arbitrary substation to occupy an upstream timeslot if the scanned table entry is empty.
The solution known from U.S. Pat. No. 5,539,743 lacks an optimal decision criterion for selecting the substation which is given the allowance to send an upstream burst in case the scanned entry in the time table is empty. In the known method, an arbitrary substation is given the allowance. This arbitrary selected substation however may have no data available for upstream transmission whereas other substations which do not get access to the free upstream timeslots have lots of data waiting to be transferred.